The invention relates generally to the field of ozone production in air or in oxygen using electrical techniques. There is a long history of ozone production including numerous patents and an extensive literature base.
Discussion of publications herein is given for more complete background of the scientific principles and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Existing electrical ozone production techniques in air and oxygen focus on coronal discharge (CD), dielectric barrier discharge (DBD), electrolytic, or UV methods. More than two hundred and fifty patents for specific apparatuses have been granted over past several decades. All of the larger ozone generators that are currently marketed use either CD or DBD techniques. Smaller generators often use inefficient UV ozone production. Electrolytic techniques are common in water environments.
There is an immediate need to improve the electrical efficiency of ozone production. Industrial applications including potable water purification, industrial water treatment, chemical processing, and agricultural treatment require continuous, large volumes of ozone. The absolute efficiency of ozone production becomes a major cost factor for these high-volume applications. In addition, the use of dry air rather than oxygen would be a major cost savings for many applications in which the absolute maximum concentration of ozone is not critical due to the energy, hardware, and maintenance costs of oxygen concentrators.
A seminal coronal discharge (CD) patent was U.S. Pat. No. 607,007 in which planar plates or screens were separated by a single glass sheet. In that case a DC voltage was applied between the two electrodes and a coronal discharge was set up with the glass as the barrier preventing a run away discharge. That patent was followed by a host of CD patents over the years. One of the key patents was U.S. Pat. No. 882,509 in which CD from metallic brush tip was described. U.S. Pat. No. 1,845,670 was the first patent in which AC voltages were clearly described and a cylindrical geometry with a single insulator and spiral inner electrode was used. U.S. Pat. No. 3,081,215 was the first patent to describe CD ozone generators with a stack of planar generators and was the first to mention the importance of no air gaps between the electrode and the insulator because of thermal losses. U.S. Pat. No. 3,891,561 described interleaved plate generators with thin, hard, bubble-free dielectric coatings and was the first to note that higher dielectric-constant insulators had improved efficiency. U.S. Pat. No. 4,213,838 described the importance of the gas flow in the generator for cooling the generator dielectric and electrodes. U.S. Pat. No. 4,417,966 recognized the importance of a low capacitance insulator to reduce dielectric losses, and was the first to describe the improvement in performance using an AC driver based on square pulses. U.S. Pat. No. 4,614,573 described the use of a higher-efficiency alumina insulator in cylindrical geometry. U.S. Pat. No. 4,619,763 in which the output ozone gas is actively cooled. U.S. Pat. No. 5,549,874 was the first patent to explicitly describe the use of sapphire insulators, but only to improve the cleanliness of the system.
A seminal dielectric barrier discharge (DBD) patent was U.S. Pat. No. 2,010,081. While that patent used only a single insulator around the inner conductor, the description and the electrical performance was typical of later DBD ozone generators. Later DBD patents had significant improvements. U.S. Pat. No. 4,079,260 was a water-cooled DBD design that clearly identified the importance of cooling the gas. U.S. Pat. No. 4,461,744 was the first patent to show an improvement in ozone generation efficiency using shorter electrical pulses (100 ns-1 μs) that generate only arc discharges while still operating in DBD mode at a rise time >20 ns.
The ozone generator described herein uses some of the techniques described in the above patents but in different embodiments and for explicitly different reasons.